WVR s for Quasar network

Transcription

1 WVR s for Quasar network Ilin G., Bykov V., Stempkovsky V., Shishikin A. Institute of Applied Astronomy, RAS St. Petersburg, Russia 1

2 Structure of presentation Sv Zc Bd Main tasks Technical features Retrieval algorithm Metrology problems Preliminary results: comparison ZWD of GNSS, WVR, VLBI Nearest plans 2

3 WVR. Main tasks Sv Zc Bd WVR s - additional instruments for "Quasar colocation sites WVR s will be used for: practically real-time ZWD monitoring, IWV / PWV monitoring VLBI data processing 3

4 WVR prototypes are installed in Svetloe observatory WVR1 (since 2011) Sv Zc Bd WVR2 (June)2013 Operation mode: zenith direction (WVR2) fully steerable (WVR1,WVR3,4,5) WVR s provide quasi - real time data rate: one count every 6 seconds 4

5 Basic requirements for WVR Sv Presence of precise MW Zc thermostable reference loads Bd Maximum temperature stability of all RF units Temperature control (and logging) of all critical points Total gain variation control of the RF units Operation mode: total power + fast switching (1kHz) of input signals Guaranteed linearity of square low detector for input signals Industry - standard electronics cheap and reliable Unified design of radiometric units Remote access and control facilities 5

6 Unified thermo stable radiometric blocks 1. DAS module: 16bit resolution ADC, 100kHz data rate, data processing (1s integration for all signals etc.) Sv 2. Ferrite Zc X-switch driver, 3 precise Bd digital thermostat drivers, 3 temperature sensors. 3. RS 485 Ferrite X-switch Cold load Radiometric Unit 21 GHz (channel A) Radiometric Unit 31GHz (channel B) Up to 20 parameters are placed into WVR log-file, 5MB/d 6

7 WVR3 design particular attention on temperature stability WVR3. (New!) Specifications: Value Frequency bandwidth 3 db, GHz Channel А 20,7±0,25 Channel B 31,4±0,25 Noise temperature, at the input, К, А 150 B 280 Gain, up to Sq. law detector, db А 65 B 65 Brightness temper. sensitivity, mк, t = 1s (Ta=10K) А 12 B 25 Relative gain instability, 24 h,, %, less than 0,03 HPBW(-3dB) / BW(-35dB) 6º / 22º Angular resolution Az, El, arc min. 5 Sv Zc Bd 7

8 Tip-cal. is used for accurate measurement of calibration signals WVR 1 in Svetloe Sv Zc Bd Temperature of Cold loads: Channel А Cold load: TcA= 313,02K± 0,02 К (r.m.s., on 1.5 year interval) Channel B Cold load: TcB = (313,38 ± 0,02) К (r.m.s., on 1.5 year interval) τ = f(1/cos(z)) opacity, tip-cal. Calibration signals referred to the WVR input: TkA = ТcA + Тrec.A (Tamb) TkB = ТcB + Тrec.B (Tamb ) Тrec.A (Tamb) receiver noise temperature depends on Tamb. 8

9 TkA, К Tip-cal. results made during the period of 10 months Sv Mean value of calibration signal Zc TkA, K, channel А Bd y = x R² = Tamb, К WVR1: ТкA = Tamb August 2012 June 2013 Ambient temperature interval: Тamb : - 20ºС +20ºС Тrec.A (Tamb) = ( Tamb ) - TcA 9

10 Retrieval algorithm {TbA, TbB } IWV P, T ZWD ZWD = Zc IWV Bd [1,2], T eff Reference: L: [cm], IWV: [g/cm 2 ], meteo: P: [hpa], T: [K] T eff, [K] atmosphere mean temperature (model based on radiosonde profiles) Now T eff can be measured (!) by T-profiler (MTP-5, ATTEX) Capacitive rain sensor data are used for WVR data correction 1. K.P.Gaikovich, N.N.Markina, A.P.Naumov, et al. Investigation of remote sensing possibilities of the low atmosphere in the microwave range and some aspects of statistical data use. Int. Journal of Remote Sensing, 1983, v.4, No.2, p A.P. Naumov (1968), vol. 4, No.2, Izvestiya, Atmospheric and Oceanic Physics. (in Russian). 10

11 Metrology: mean atmosphere temperature measurement + calibration IWV Svetloe 27 Feb 2014, (UT: 05:20), T(h) Zc Bd Atmosphere temperature profiler MTP-5: Measurements of T(h) with MTP-5: T(h) Teff 11

12 Data processing : structure of software package Zc Bd Software 12

13 ZWD, [mm] r.m.s. of dl ~ 3 mm (dl= ZWD(WVR1)- ZWD(GNSS)) WVR1 GNSS (GPS) VLBI ("QUASAR") Zc Bd 50 "WVR1" 40 "dl(gnss_wvr1)" : : : : : :00 13

14 Seasonal stability of dl= ZWD(WVR1)- ZWD(GNSS) Svetloe ZWD (WVR1- GNSS) Bias: 1mm, r.m.s. ~ 5 мм, (~25% data removed) Small temperature dependence Zc Bd Interval: from to (301 days) (~20% data removed : rainfall, snowfall, maintenance) 14

15 Experimentally confirmed results Zc WVR1: Bd Stable metrological parameters for a year period large interval between calibrations low operational expenses continuous, reliable, maintenance-free operation for several months interval Nearest plans: installation MTP-5 in Zelenchukskaya, installation WVR s in Zelenchukskaya and Badary 15

16 Zc Bd Thank you for your attention! 16